Mutator — game modification that modifies only small part of game. As opposed to mods that can’t be mixed (only one can be active at the same time) you may add few mutators in game simultaneously.

There are four most common mutator types in Killing Floor:

1. Mutator itself. It modifies specific game rules (armor welding ability, enchanced scoreboard) 2. Weapon mutator. It adds new weapon to game (Hunting Rifle, PortalTurret) 3. Zed mutator. It adds new specimen to game (Brute, HellFire) 4. Character mutator. It adds new playable character model to game (Stig)